Known are various types of processes for producing unsaturated aliphatic aldehydes such as acrolein and methacrolein by the catalytic oxidation of olefins such as propylene and isobutylene in a vapor phase with molecular oxygen at an elevated temperature. Also, various types of catalysts effective for the above-mentioned processes are known. In connection with such known processes and catalysts, it is believed that, in general, the production of methacrolein from isobutylene is more technically difficult than that of acrolein from propylene. In fact, it is known that when acrolein and methacrolein are produced respectively from propylene and isobutylene by using the same type of catalyst which is believed to be effective for catalytically converting olefins into corresponding unsaturated aliphatic aldehydes, the yield of methacrolein is usually lower than that of acrolein. For example, Japanese Patent Application Publication No. 47-42813(1972) states that the yield of methacrolein is 5 to 10% below that of acrolein. In this connection, it is presumed that the difference in yield between methacrolein and acrolein is derived from the fact that the methacrolein molecule has a branched carbon chain, that is, a methyl group, which is not contained in the acrolein molecule. Therefore, it is considered that, in order to convert isobutylene catalytically into methacrolein in a high yield, a new type of catalyst different from conventional catalysts effective for the catalytic oxidation of propylene into acrolein, should be provided.
The conventional catalysts for catalytically converting isobutylene into methacrolein usually contain as catalytic ingredients, molybdenum, bismuth, iron, cobalt and an alkali metal such as potassium (Mo-Bi-Fe-Co-K). This type of conventional catalysts is disclosed, for example, in Japanese Patent Application Publication No. 47-42813(1972) (Co-Fe-Bi-W-Mo-Si-K-P-O), Japanese Patent Application Publication No. 48-17253(1973) (Ni-Co-Fe-Bi-P-Cs-K-Mo-O), U.S. Pat. No. 3,966,823 (Ni-Co-Fe-Bi-P-K-Mo-O), U.S. Pat. No. 4,049,577 (Co-Fe-Bi-Mo-K-O), U.S.Pat. No. 3,825,502 (Co-Fe-Bi-Mg-K-Mo-O), Japanese Patent Application Publication No. 51-47684(1976) (Co-Fe-Bi-Cr-K-Mo-O), Japanese Patent Application Laying-open No. 48-52713(1973) (Co-Fe-Bi-Cs-K-Mo-O) and Japanese Patent Application Laying-open No. 51-34107(1976) (Mn-K-Ni-Co-Fe-Bi-Mo-O).
The above-mentioned types of conventional catalysts can enable methacrolein to be produced in a yield of approximately 70%. However, this level of yield is not high enough for industrial use.
Also, it was discovered by the inventors of the present invention that the conventional catalysts have relatively poor resistances to attrition and compression and also exhibit a relatively poor durability in resistances to attrition and compression. Therefore, the conventional catalysts are often disintegrated during the catalytic oxidizing operation. The disintegration of catalysts results in a reduction in the catalytic efficiency of the catalysts.
Under these circumstances, it is desired to provide a new type of catalyst which enables methacrolein to be produced in a high yield and which exhibits an enhanced mechanical strength and durability.
As a result of a study on the improvement of the catalyst, it was discovered by the inventors of the present invention that the catalytic efficiency and the mechanical strength and durability of the catalyst can be enhanced by using cesium as an alkali metal catalytic ingredient and by adding an additional catalytic ingredient consisting of at least one member selected from the group of vanadium and palladium, to the conventional catalytic ingredient, that is, molybdenum, bismuth, iron, cobalt and an alkali metal.
Furthermore, it was discovered by the inventors that the catalytic efficiency and the mechanical strength and durability of the above-mentioned catalyst can be further improved by adding an additional catalytic ingredient consisting of at least one member selected from titanium, nickel, tin and zirconium to the above-mentioned conventional additional catalytic ingredients.
The present invention is based on the above-mentioned discoveries.